1. Field of the Invention
This invention relates to an apparatus and method for encoding a moving image.
2. Description of the Related Art
The widespread use of broadband networking has actively encouraged the distribution of video and audio stream over the Internet. The stream distribution has been used for various types of Internet services, such as Internet telephone, remote television conference, chat or the like. The chat system using an audio/video stream allows one user to transmit her/his facial image and/or voice to another user in a remote location over the network. The users can replay the each other's moving image and voice on their terminal so that they can chat with each other as if they were together in the same place.
The video stream distribution can be realized in the following procedure. A video stream is generated in which each frame of the moving image is compression-encoded in accordance with a moving image encoding method such as MPEG (Moving Picture Experts Group), H.264/AVC (Advanced Video Coding) or the like. Then the video stream is packetized into IP (Internet Protocol) packets and the packets are transferred over the Internet and received at the communication terminal of the user. Since the Internet transmits packets on a best effort basis, if the network is congested, some of the packets could be discarded or delayed resulting in data deficiency so that the frame image could not be received properly.
Japanese Patent Application Laid-Open No. 2001-57672 discloses a communication device that communicates image data and audio data with a plurality of the other communication devices.
If a chat system is configured to use video and audio via the Internet, the IP packets could be lost at a few percents level even in a normal situation so that at least a part of a frame of the video code stream might be possibly lost and the frame could not be decoded properly. The real-timeliness is the most important factor in such a chat system and it could be fatal that the reproduction quality of the motion image is degraded because of such frame dropping. In the video stream distribution, if frame dropping occurs, the receiver could request the sender to retransmit the dropped frame so as to receive the dropped frame again from the sender. However, even if the retransmitted frame were reproduced, the delay would grow, the real-timeliness might be lost and the system could not meet requirements on quality of the reproduced moving image, especially for a time-critical application such as a chat system. Furthermore, since the sender side needs to store the frames that have been transmitted in order to retransmit the frames, an additional capacity of memory will be required for the retransmission purpose.